Acute and obtuse angles: what children learn
In this game children sort angles into acute, right angle and obtuse, using clock hands, shape corners and turns. An acute angle is less than a right angle. An obtuse angle is greater than a right angle but less than a straight line.
Supports part of Common Core 4.G.A.1: right, acute and obtuse angles. This focused game does not cover the entire standard.
Common Core connection: 4.G.A.1. This is focused practice for part of the standard.
How to play
Sort the cards into the right groups. Tap a card, then its group. You can also drag a card, or press the number on its group. Each game has 3 rounds with no timer. Every card is checked as soon as you place it: a card in the wrong group comes back with a hint, and you get a point for each card you place right first time. For a quicker go, choose Quick quiz: 10 multiple-choice questions in 150 seconds (choose Relaxed for more time).
Step by step
- Start with a right angle. Compare each angle with a square corner.
- Acute. If the angle is smaller than a right angle, it is acute.
- Obtuse. If it is bigger than a right angle but less than a straight line, it is obtuse.
- Order angles. Put acute angles first, then right angles, then obtuse angles.
Worked examples
Example 1: The angle between clock hands at 2 o'clock
Working: Smaller than a right angle.
Answer: acute
Example 2: The angle between clock hands at 3 o'clock
Working: Exactly a square corner.
Answer: right angle
Example 3: The angle between clock hands at 4 o'clock
Working: Wider than a right angle, but less than a straight line.
Answer: obtuse
Common mistakes and how to fix them
- Mixing up the words acute and obtuse. Acute angles are 'a cute' little angles. Obtuse angles are the wide ones.
- Judging size by arm length. Draw two angles the same size with different arm lengths and compare.
- Calling a straight line an obtuse angle. A straight line is two right angles. Obtuse angles are less than that.
Activities to try at home
- Make angles with arms or with two pencils and name them.
- Spot acute and obtuse angles in the letters of a name.
- Use the hands of a clock to show an acute and an obtuse angle.
Ideas for the classroom
- Students order a set of drawn angles from smallest to largest.
- Give students a shape and ask them to label each angle as acute, right or obtuse.
- Make angles with geostrips and challenge a partner to name them.
Free printable game and worksheet
The free printable starts with a game sheet, such as a color-by-answer picture, an answer maze or a secret-code joke, followed by a worksheet. Both use the same checked questions as the online game, and the answers are on the last page. Print it, or save it as a PDF from your browser’s print menu.
Open the free printable game and worksheet
Frequently asked questions
How should I choose this game for my learner?
Supports part of Common Core 4.G.A.1: right, acute and obtuse angles. This focused game does not cover the entire standard.
Can it be played with a keyboard?
Yes. Tab to a card, press Enter to pick it up, then choose the group it belongs in.